ambassador stevens first thought to be an impulsive act by angry mob. outraged over anti-muslim film. but today high ranking american officials admitted it was the work of terrorists. abc news reporter jake tapper has the latest on the story. >> secretary of defense panetta acknowledged that the attack that killed 4 americans in benghazi libya on the anniversary of 9/11 was not only carried out by terrorists. it was premeditated. >> as we determined the details of what took place there, and how that the attack took place, that it became clear that there were terrorists who had planned that attack. >>reporter: white house first suggested that the benghazi attack was spontaneous. the result of that anti-muslim video inciting mob throughout the region. >> must be mostly clear that these protests were in reaction to a video that had spread to the region. we don't know otherwise. the we have no information to suggest that it was a pre-planned attack. >>reporter: but sources tell abc news that intelligence officials on the ground medley suspected the attack w